Looks like the moons of Uranus could form from a circumplanetary disc, despite the relatively low masses of the ice giant planets, as opposed to requiring some kind of collision. This also suggests that the pre-Triton satellite system of Neptune might have looked something similar to the regular satellites of Uranus. The distributions look like they get up to a few 10-3 of the planetary masses, so maybe at a stretch it would be possible to find Mars-mass icy moons around extrasolar ice giants.